1. Field of the Invention
The present invention relates to a photographic material and, more particularly, to a photographic material comprising a support with a hydrophobic surface having thereon a photographic layer comprising a hydrophilic colloid.
2. Description of the Prior Art
Heretofore, polyethylene terephthalate, cellulose triacetate, polystyrene, polyolefin-laminated paper, and the like have been used as a photographic support due to their excellent transparency, flexibility, etc. However, it has been extremely difficult to strongly adhere a photographic layer comprising a hydrophilic colloid (represented by gelatin) to these supports due to the highly hydrophobic nature of the surface of these supports.
As processes for obtaining adhesivity between a support and a photographic emulsion layer through a surface treatment, particularly, treatments to render the surface of a hydrophobic support hydrophilic, i.e., processes which have been attempted in the prior art so as to overcome the above-described difficulty, the following two processes have been employed (for example, as disclosed in U.S. Pat. Nos. 2,698,241, 2,764520, 2,864,755, 2,864,756, 2,972,534, 3,057,792, 3,071,466, 3,072,483, 3,143,421, 3,145,105, 3,145,242, 3,360,448, 3,376,208, 3,462,335, 3,475,193; British Pat. Nos. 788,365, 804,005, 891,469, etc.):
(1) a process for obtaining adhesivity by subjecting the support to a surface-activating processing such as chemical processing, mechanical processing, corona discharge processing, flame processing, ultraviolet light-processing, high frequency processing, glow discharge processing, active plasma processing, laser processing, mixed acid processing, ozone-oxidizing processing, or the like, and directly coating thereon a photographic emulsion; and
(2) a process of subjecting the support to the above-described surface processing, providing a subbing layer on the support, and coating thereon a photographic emulsion layer.
Of these two processes, process (2) is more effective and widely employed.
The above-described surface processings appear to render the surface of a normally hydrophobic support hydrophilic through formation of polar groups on the surface and, as a result, the affinity for the polar groups of the components contained in a subbing layer is increased.
Also, various techniques have been developed for coating a subbing layer on a support. These techniques basically involve two coating processes; a so-called double layer process which comprises providing a layer adhering well to the support as a first layer and coating on this first layer a hydrophilic resin layer as a second layer; and a single layer process which comprises coating only one resin layer containing both hydrophilic groups and hydrophobic groups on a support.
These processes have been studied in detail, and the adaptability of many resins including copolymers prepared from monomers such as vinyl chloride, vinylidene chloride, methacrylic acid, acrylic acid, itaconic acid, maleic anhydride, etc., polyethyleneimine, epoxy resins, grafted gelatin, nitrocellulose, and the like have been examined. However, unavoidably these processes have the following defects.
(A) Insufficient adhesion strength
That is, the above-described surface-activating processing (1) alone fails to provide satisfactory adhesion strength for practical photographic materials particularly where polyethylene terephthalate, polystyrene, etc., are used as a support. Also, even when a subbing layer is provided on the support, sufficient adhesion strength cannot be obtained, since resins which have a good affinity for a hydrophobic support and adhere well to a hydrophobic support generally have poor affinity for a hydrophilic photographic layer to be coated thereon. Conversely, when a hydrophilic resin having a good affinity for a photographic layer is coated as a subbing layer, there is the defect that this layer does not adhere well to the support even though it adheres well to the photographic layer.
(B) Subbing requires many steps and much time.
Since gelatin is widely used as a resin employed as a binder of a photographic layer, coating and drying of photographic layers are conducted by drying at an extremely low temperature (for example, initially cooling to about 10.degree. C. or less, and then drying at about 50.degree. C. or less) utilizing the special property of gelatin of gelling at a low temperature. However, in providing a subbing layer using the above-described polymers, it is necessary to heat to an elevated temperature to dry after coating (about 100.degree. C. or above) due to the lack of the ability to gel at a low temperature. Furthermore, as to the solvent, while water can be used for gelatin, organic solvents are often used for these synthetic high polymer compounds, and hence coating of the polymers requires a coating machine for organic solvents different from that for coating photographic layers. In addition, in the case of subbing double layers, the steps of coating and drying must be repeated two or three times.
(C) Problems of toxic gases, stimulation on skin and environmental pollution.
A solvent which is capable of swelling or dissolving the support, a so-called etchant, and which has a high polarity, has a high boiling point and is expensive, has been incorporated in a large amount in order to enhance adhesivity of the above-described subbing layer. As etchants for polyesters, compounds having an aromatic nucleus (a benzene ring, a naphthalene ring, a pyridine ring, a pyrrole ring, a fused ring thereof, or those rings substituted with one or more of an alkyl group, an alkoxy group, an acyl group, a nitro group, a cyano group, a halogen atom, a hydroxy group, a formyl group, a carboxy group, an alkoxycarbonyl group, a hydroxyalkyl group, an aminoalkyl group, a haloalkyl group, etc., as substituents), alcohols, ketones, carboxylic acids, esters, aldehydes, and the like (see, e.g., British Pat. Nos. 772,600, 776,157, 785,789, 797,425; U.S. Pat. No. 2,830,030; German Pat. Nos. 1,020,457, 1,092,652, etc.) have been used. To be specific, the following compounds are known, for example, benzoic acid, salicylic acid, salicylic acid esters, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, methanesulfonic acid, trifluoromethanesulfonic acid, nitropropanol, benzyl alcohol, benzaldehyde, acetylacetone, acetylphenol, benzamide, benzonitrile, anisole, nitrobenzyl alcohol, chlorobenzyl alcohol, pyrrole, chloral hydrate, benzylamine, xylylenediamine, nicotinic acid amide, nicotinic acid ester, and the like.
In addition to these, compounds, already well known and commonly used, include those compounds which have a phenolic hydroxy group or groups, such as phenol, o-chlorophenol, p-chlorophenol, dichlorophenol, phenylphenol, chlororesorcin, phloroglucin, orcinol, pyrogallol, gallic acid, o-cresol, m-cresol, p-cresol, resorcin, methoxyphenol, etc.
However, these etchants are generally difficult to handle and are well known to be toxic to humans. Of the compounds, phenolic compounds have such a strong stimulation and permeability on skin that they involve serious working problems. Furthermore, complete recovery is indispensable, since contamination of these substances in discharged waste water and off-gas would cause environmental pollution. This requires additional equipment.
(D) Support planarity is deteriorated.
As is described in items (B) and (C) above, considerably elevated temperatures are necessary in the prior art to dry the subbing layer. In particular, when phenolic compounds are used, the drying of a subbing layer requires quite a long time since they generally possess a high boiling point of 180.degree. C. or higher. Therefore, during the drying step, in particular in the initial stage thereof, a swelling of the polyester and a reduction in elasticity due to an increase in the degree of crystallization occur because of the permeation of the solvent into the support and, in the latter stage, contraction of the polyester occurs. Thus, planarity is seriously damaged.
(E) Temperature control in the step of drying the subbing layer is difficult.
Also, in general, the etching ability of a solvent is greatly dependent upon temperature, and hence, when adhesivity is attained by an anchor effect of the resin to the support, the adhesivity itself is greatly dependent upon the temperature employed in the steps of coating, drying, and the like.
This is an extremely serious problem from the standpoint of stable production.